NFL/NBA now have a Donald Sterling problem with Gayle Benson
Louisiana is a right-to-work state. Unless he had a personal services contract with the Bensons, he can be terminated with no explanation from the employer.
"We're making a change and your services are no longer required."
That's it. History.
His request for back pay needs to be addressed in any personal services contract (if one existed) he and the Bensons agreed upon.
The accusation of racial slurs is just that; an accusation. If he has audio/video/written correspondence to corroborate this claim, then that is an entirely different matter.